Preventing overdrying of terminal portions in continuous drying systems



Feb.. il, 194?. f R M SCHAFFNER 2,415,445

PREVBNTING OVERDRYING OFTERMINAL PORTIONS f INA CONTINUOUS DRYING SYSTEMS Filed NOV. 22, 1945 Patented Feb. 11, 1947 PREVENTING OVERDRYING' OF TERMINAL PORTIONS IN CONTINUOUS DRYING SYS- TEMS Robert M. Schaffner, Chicago, Ill., assignor to The Guardite Corporation Application November 22, 1943, Serial No. 511,346

(Cl. SLI- 15) 4 Claims. l

This invention relates to a method of avoiding overdrying or scorching of heat susceptible products in a continuous drying system.

When heat susceptible materials, such as foods, are dried in modern vacuum equipment, it is customary to use a continuous system in which progressive increments of material to be dried are introduced at one end of a long chamber and removed at the other end. Within the chamber drying is preferably accomplished under low absolute pressure in an atmosphere of steam and with radiant heat as a major source of drying energy.

While a system of this type is designated as continuous, it is in reality semi-continuous in that the amounts of any given product treated are limited and the device may not be operated beyond an eight-hour day or it may be shut down at intervals of days. In any case it has been found that the terminal portions of the train of product are customarily overdried and usually scorched because of the fact that the heat available is more than sufficient at the terminal periods and no ready method of adjusting radiant heat and steam input has been found which'will take care of this factor,

In accordance with the present invention the diiiculty is overcome in a very simple and eiective manner by introducing into the drying progression, at each end of the progression, a substantial amount of a moistened material which is either not heat sensitive or is of such little value that overdrying or overheating of the material does not matter.

The invention is illustrated diagrammatically in the drawing "in Which is shown an elongated chamber Il! having an inlet door l l, an outlet door l2 and a series of tray levels I3. Trays lll are advanced seriatirn along these levels. The first trays in each lever are provided with moisn tened waste material l5 and the succeeding with moist heat susceptible material I6 to be dried. The chamber may be evacuated through line Il while superheated steam is introduced at I8 and I9. Heating coils, not shown, are disposed under and over each tray level. A lock 20 is provided at each end of the chamber.

For example, in a system in Which the product is introduced in thin layers in a series of trays, as described in Heineman application 501,399, iiled September 3, 1943, it has been found preferable to place in one or more of the trays in each row a paper material such as 1/8 inch beaver board and saturate this material with water.

Therefore, in the operation of the system, when the drying chamber is to be put into operation, the heating coils and vacuum and superheated steam conditions are established as closely as possible to those desired, and then the trays are introduced, but the rst tray or series of trays in each tier, if there is more than `one tier, is provided with the mois-tened paper material as described. This is immediately followed by trays iilled with product to be dried and the progression ismaintained in the usual fashion until for one reason or another it is to be terminated. The progression is then closed with one or more trays in each layer similarly provided with moistened waste material.

Sometimes it is desirable to provide more than one tray full of Wet material. However, with trays approximately 5 to 6 feet in Width, and l to 11/2 feetl across, and employing a chamber holding 'vertical rows of trays, and 50 to 60 feet in length, 8 trays full of moistened waste material in each tier have been found sufficient.

The effect of the moistened Waste material at the opening of the progression is relatively easy to understand. Apparently the non-heating parts of the apparatus, such as the tray supports and the conveyors, become undesirably warm in the absence of wet material. The moistened waste Imaterial preceding the food products to be dried, cools such parts suiciently to produce normal operating conditions or at least conditions suciently approaching normal that the deviation is not critical. In any system the amount, area, and degree of wetting of such material are correlated to bring the system into equilibrium.

At the end of the progression the effect is more indirect. There, the non-heating parts tend to become hotter after the food product being dried has passed beyond them, and the extra moist Waste material serves to prevent this from happening. The overheating of these portions of the apparatus after the food has passed through them has no direct eiect but indirectly serves to bring the superheated steam atmosphere to a higher temperature than is desirable.

The moistened Waste material actually produces better results than if food material were passed through the drier and permitted to scorch. This is apparently because the amount of moisture available is actually made greater than would be available in a similar space of food material, and, therefore, is able to bring the heat balance into equilibrium, whereas the food material has no such surplus.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom.

What I claim as new and desire to secure by Letters Patent is:

l. The method of drying a moist organic food product inwhich the product to b e dried is introduced to and removed from an elongated drying chamber in progressive increments at least dried is introduced to and removed from an elongated drying chamber in progressive increments as great in aggregate as the capacity of the chamber and is dried therein under Vacuum; characterized by introducing into the drying chamber at a terminus of the progression of increments, a substantial quantity of moistened material different from the organicifood product and passing such material through the chamber as a terminus of the progression of increments, and drying it together with the organic food product to be driedtherein, whereby overdrying of said terminal food product is avoided.

3. The method as set forth in claim 2, in which said moistened material is supplied both at the beginning and at the end of the progression of increments.

4. The method as set forth in claim 2, in which said moistened material is wet paper,

ROBERT M SCHAFFNER. 

